Great War Telephone Equipment 1914-1918:

Telephone Set Portable D Mk. III

Signalling Officer and his men, seen here using the D Mk 3 field telephone to phone through details of enemy movements from an observation point in the roof of an old barn.

 

Great War D Mk 3 Field Telephone set, showing Morse Key, Folding handset and watch receiver, all mounted in a leather carry case and strap.

Telephone Set Portable D Mk. III

The standard portable buzzing telephone set in the service is the DIII. It can be used for sending messages by Morse code (for which purpose a key is provided) or for speaking. The set consists of the instrument itself, which is contained in a metal or ebonite case, a telescopic hand telephone, and a separate head receiver. The whole is carried in a leather case.

the instrument case is divided into two parts, which are separately accessible. The back one contains two "S" type dry cells, fitted with spring contacts. The battery is used for both buzzing and for speaking. The front compartment contains the buzzer (which is of special design,being polarised) and the insulating condenser. On the lid are fixed the sending key, the connections for hand and head telephones, and the three terminals, marked L, L or E, and CL.

The CL terminal is intended to be used instead of the L terminal when tapping in on telegraph line. By using this terminal a condenser is inserted between instrument and the line. The function of this condenser is to insulate the telephone from the line as far as direct currents are concerned, and at the same time to permit the passage of the alternating buzzing and speech currents.

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Guy Smith     e mail:    guy@trenchmap.com